The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Abbott backs citizenship decision

Prime Minister Tony Abbott has ducked a question about whether he is chasing down a cabinet leak, saying his government is committed to national security.

Opposition Leader Bill Shorten on Tuesday asked Mr Abbott what steps he is taking to identify ministers who leaked to the media about rifts over a proposed plan to take citizenship off Australians engaged in terrorism.

"Anyone who raises a gun or a knife to Australians simply because of who we are and the values we have has forfeited his or her right to consider himself one of us," Mr Abbott told parliament.